Breast cancer is the second most common cancer among women in the U.S., with an estimated 207,090 new diagnoses in 2010 and a lifetime risk among women born today of 1 in 8. Most breast cancer cases are diagnosed among postmenopausal women at an early and treatable stage, and most of their tumors (70-80%) are hormone-receptor positive. For these women, standard adjuvant endocrine treatment is aromatase inhibitor (AI) therapy to prolong disease-free survival and time-to-recurrence. Unfortunately, joint pain/stiffness/ achiness is a common side-effect of AIs, with estimates of joint complaints ranging from 46% to 74% among survivors seen in clinical practice. The precise etiology of AI-associated musculoskeletal symptoms (AIMSS) remains unclear and is complicated by the high prevalence of benign and non-specific musculoskeletal symptoms in the general population of older women, such as arthritis. AI discontinuation due to side-effect severity is an estimated 20-32%, and is of great concern among oncologists. Research is needed to identify effective, easy-to-use, sustainable, and safe alternative or adjunct approaches to AIMSS management, so that breast cancer survivors are able to remain on AI therapy and have a life that is as pain-free as possible. We propose to investigate whether moderate-intensive physical activity (PA) can provide relief from AIMSS within a sample of female breast cancer survivors on AI therapy who report moderate to severe joint symptoms. Specifically, we propose to adapt and test the Arthritis Foundation's Walk With Ease (WWE) program, which is evidence-based for reducing joint pain, stiffness and fatigue among adults with arthritis and is available in a self-directed (non-group) format. Our proof of concept hypotheses are that: (a) it is feasible to adapt WWE for our target patient population and (b) that an adapted WWE can provide joint pain/symptom relief for patients with AIMSS similar to that of adults with arthritis. To investigate these hypotheses, we propose to: (1) develop an initial adaptation of WWE-Breast Cancer (WWE-BC) based on interviews with breast cancer survivors (N=20) focused on barriers and facilitators to engaging in PA; (2) conduct a preliminary assessment of the effect of WWE-BC within a new sample of survivors (N=60) with regard to (a) engaging in PA, (b) managing joint pain/symptoms and (c) remaining on AI therapy; and (3) develop WWE-BC messages and communication strategies based on interviews with survivors and oncology physicians, nurse practitioners and nurse navigators. Data on the acceptability, feasibility, safety and promise of WWE-BC gathered through this study will inform the development of a larger study to test the effectiveness of WWE-BC, identify potential effect mediators and/or moderators, and establish generalizability. All aspects of our study will be informed by Patient Advisors who are part of our Study Team as well as by oncologists who are actively engaged in the design, implementation and analysis of our study.